The present invention relates to a spring connector used for surface mounting in an electronic device, and method for manufacturing the spring connector.
As a method for connecting electric parts in an electronic equipment such as a portable telephone to a circuit substrate, a spring connector having a plunger which is slidably mounted in a tube and outwardly urged by a spring is used. The spring connector is secured to the circuit substrate and the plunger is pressed against a terminal electrode of the electric part in assembling process of the part in the equipment, thereby electrically connecting the part to the circuit substrate.
FIG. 8 shows a conventional spring connector of an electronic equipment, and FIG. 9 is a sectional view of the spring connector.
The spring connector 1 comprises a cylindrical tube 2 made of metal, and a metal plunger 3 slidably inserted in the tube 2 and outwardly urged by a coil spring 7. A shoulder of a flange 3a of the plunger 3 is pressed against a bent edge 2a of the tube 2 by the spring 7.
As shown in FIG. 8, the tube 2 is secured to a circuit substrate 4 by a solder 5. An electric part 6 is downwardly moved in the direction shown by an arrow at the assembling process of the electronic equipment, and a terminal electrode 6a of the part 6 is elastically pressed against the plunger 3 by the coil spring 7, so that the part 6 is electrically connected to the circuit substrate 4.
The underside of the flange 3a is inclined so that the peripheral wall of the flange is pressed against the inner surface of the tube 2 in an inclined condition. Thus the flange is strongly pressed against the inner surface, thereby ensuring the electrical conductivity between the tube and the plunger.
FIG. 10 is a sectional view showing another conventional spring connector. A plunger 3A is also hollow to form a space 3b. The spring 7 is inserted in the space 3b. 
Japanese Patent Application Laid Open Publication 2002-25657 discloses another spring connector. The spring connector also has a plunger urged by a coil spring.
In the connector shown in FIG. 9, the plunger 3 occupies a considerable length of the spring connector. The length of the coil spring 7 is limited to a short length. Consequently, the stroke of the spring can not be increased.
In the spring connector of FIG. 10, although the length of the coil spring is longer than that of the coil spring of FIG. 9, the underside of the flange 3a of the plunger 3A is not inclined unlike the plunger of FIG. 9. Therefore, the flange 3a is not pressed against the inside wall of the tube 2 at a higher pressure. Therefore, contact resistance between the flange and the inside wall of the tube is low, so that the operation of the plunger becomes unstable. If the gap between the flange and the inside wall is reduced, the operation becomes stable. However, it is severe and disadvantageous for manufacturing the connector to process the connector having a small gap.
A common problem to both spring connectors of FIGS. 9 and 10 is the fact that both connectors are made of metal. Consequently, since the heat of the spring connector quickly drops, it is difficult to melt solder on the connector at reflow process of the solder. As a result, the quality of the solder process decreases.
On the other hand, since an electronic part of electronic equipment such as an IC and capacitor generally has a flat surface, the part is supplied to a mounting position by vacuum sucking. However, since each of the spring connectors of FIGS. 9 and 10 has not a flat surface, the connector can be treated by vacuum. Therefore, the connector must be treated by a special mounting device, which causes the number of steps to increase.
In the assembling step, the coil spring 7 is inserted in the tube 2, the plunger 3 is inserted in the tube, an upper portion of the tube must be staked to hold the flange 3a. The coil spring must be assembled one by one, which causes the manufacturing cost to increase.